An engine of a vehicle may be automatically stopped during selected operating conditions to conserve fuel. The engine may be subsequently automatically restarted when operating conditions change, when a brake pedal is released for example. A transmission may also be coupled to the engine to deliver torque from the engine to vehicle wheels. In some examples, the transmission may be an automatic transmission that includes few or no direct operator inputs to directly adjust the operating state of the transmission. In other words, the operator may not be able to manually control transmission clutches and gears. Instead, transmission clutches and gears may be adjusted by a controller that accepts inputs from the operator and ancillary sensors. If the transmission is controlled in an undesirable manner during automatic engine stops and starts, the transmission may degrade at a rate that is higher than is desired.
The inventors herein have recognized the above-mentioned disadvantages and have developed a method for operating a vehicle powertrain, comprising: adjusting a position of a clutch of a transmission in response to a battery current during cranking of an engine while starting the engine.
By adjusting a position of a clutch in response to battery current during cranking of an engine while starting the engine, it may be possible to reduce transmission degradation and improve vehicle launch during automatic engine stops and starts. Specifically, battery current may be sensed during engine cranking and compared to a threshold current. If the battery current is greater than the threshold current, then the force being applied by the clutch may be reduced. On the other hand, if less than a desired amount of engine torque is transferred through the transmission during engine cranking, then force applied by the clutch may be increased to improve vehicle launch.
The present description may provide several advantages. For example, the approach may reduce transmission degradation. Further, the approach may improve vehicle launch by reducing lag time between when the engine is started and when engine torque is delivered to vehicle wheels. In addition, the approach may improve battery life via reducing current draw from the battery during engine cranking.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.